MONDAY, Nov. 26 (HealthDay News) -- Genes specific to the X chromosome are among newly identified genes linked to rheumatoid arthritis and could help explain why women are more likely than men to develop the disease, researchers say.

Women have two X chromosomes while men have an X and a Y chromosome.

The X-chromosome-specific genes were among 14 newly identified genes in both women and men that can lead to rheumatoid arthritis, adding to the 32 genes previously pinpointed by the researchers at the Arthritis Research U.K. Epidemiology Unit at the University of Manchester and their colleagues.

It is believed that these 46 genes account for the vast majority of genes associated with rheumatoid arthritis. The research could lead to new treatments for the disease, according to the study published online recently in the journal Nature Genetics.

"This groundbreaking study brought together scientists from around the world and involved the use of DNA samples from more than 27,000 patients with rheumatoid arthritis and healthy controls," study lead author Jane Worthington, professor of chronic disease genetics at the University of Manchester, said in a university news release. "As a result of our findings, we now know that genetic variations at over 45 regions of the genome determine susceptibility to this form of arthritis."

Rheumatoid arthritis is different from osteoarthritis, the arthritis associated with aging and wear and tear. It frequently starts between the ages of 25 and 55, and causes inflammation in the joints, resulting in swelling, stiffness, pain and reduced joint function.

Lifestyle and environmental factors such as smoking, diet, pregnancy and infection are believed to play a role in rheumatoid arthritis, but a person's genes also influence their risk for the disease. The condition affects about 1 percent of the world's population.

"This work will have a great impact on the clinical treatment of arthritis; we have already found three genes that are targets for drugs, leaving a further 43 genes with the potential for drug development, helping the one-third of patients who fail to respond well to current medications," study first author Dr. Stephen Eyre said in the news release.

"This is the first time that a genetic association has been established between rheumatoid arthritis and the X chromosome," Alan Silman, medical director of Arthritis Research U.K., said in the release. "This could provide a useful clue in helping us to understand why rheumatoid arthritis is three times more likely to occur in women."